Method of monitoring membrane separation processes

ABSTRACT

Methods and systems for monitoring and/or controlling membrane separation systems or processes are provided. The present invention uses measurable amounts of inert fluorescent tracers and tagged fluorescent agents added to a feed stream to evaluate and/or control one or more parameters specific to membrane separation such that performance thereof can be optimized. The methods and systems of the present invention can be used in a variety of different industrial applications including raw water processing and waste water processing.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

[0001] This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 10/109,260, filed Mar. 28, 2002, now pending.

FIELD OF THE INVENTION

[0002] This invention relates generally to membrane separation and, moreparticularly, to methods for monitoring and/or controlling membraneseparation processes.

BACKGROUND OF THE INVENTION

[0003] Membrane separation, which uses a selective membrane, is a fairlyrecent addition to the industrial separation technology for processingof liquid streams, such as water purification. In membrane separation,constituents of the influent typically pass through the membrane as aresult of a driving force(s) in one effluent stream, thus leaving behindsome portion of the original constituents in a second stream. Membraneseparations commonly used for water purification or other liquidprocessing include microfiltration (MF), ultrafiltration (UF),nanofiltration (NF), reverse osmosis (RO), electrodialysis,electrodeionization, pervaporation, membrane extraction, membranedistillation, membrane stripping, membrane aeration, and otherprocesses. The driving force of the separation depends on the type ofthe membrane separation. Pressure-driven membrane filtration, also knownas membrane filtration, includes microfiltration, ultrafiltration,nanofiltration and reverse osmosis, and uses pressure as a drivingforce, whereas the electrical driving force is used in electrodialysisand electrodeionization. Historically, membrane separation processes orsystems were not considered cost effective for water treatment due tothe adverse impacts that membrane scaling, membrane fouling, membranedegradation and the like had on the efficiency of removing solutes fromaqueous water streams. However, advancements in technology have now mademembrane separation a more commercially viable technology for treatingaqueous feed streams suitable for use in industrial processes.

[0004] Further, membrane separation processes have also been made morepractical for industrial use, particularly for raw and wastewaterpurification. This has been achieved through the use of improveddiagnostic tools or techniques for evaluating membrane separationperformance. The performance of membrane separation, such as efficiency(e.g. flux or membrane permeability) and effectiveness (e.g. rejectionor selectivity), are typically affected by various parameters concerningthe operating conditions of the process. Therefore, it is desirable tomonitor these and other types of process parameters specific to membraneseparation to assess the performance of the process and/or the operatingconditions. In this regard, a variety of different diagnostic techniquesfor monitoring membrane separation processes have been routinely usedand are now understood and accepted as essential to its practicality andviability for industrial use.

[0005] However, monitoring is typically conducted on an intermittentbasis, for example, once a work shift or at times less frequently. Knownemployed monitoring techniques can also be labor and time intensive.Thus, adjustments made to membrane separation processes in order toenhance performance based on typical monitoring may not be made in anexpeditious manner. In addition, the presently available monitoringtechniques often do not provide optimal sensitivity and selectivity withrespect to monitoring a variety of process parameters that are generallyrelied on as indicators to evaluate and/or control membrane separationprocesses.

[0006] For example, monitoring techniques typically applied to reverseosmosis and nanofiltration include conductivity measurements and flowmeasurements. Conductivity measurements are inherently less accurate inorder to determine the recovery of solutes which are substantiallyretained by the membrane. In this regard, conductive salts, typicallyused as an indicator during conductive measurements, can pass throughthe membrane. Since salts generally pass through the membrane as apercentage of the total salt concentration, changes in localconcentration due to concentration gradients or the like can change theconductivity of the product water without necessarily indicatingmembrane damage. This is especially true in the last stage of amulti-stage cross flow membrane system where salt concentrations (and,therefore, passage of salts as a percentage of that concentration) reachtheir highest levels. In this regard, the salt passage/percent rejectionparameter is generally determined as an average value based on valuesmeasured during all stages of the membrane system.

[0007] Further, flow meters generally employed in such systems aresubject to calibration inaccuracies, thus requiring frequentcalibration. Moreover, typical monitoring of reverse osmosis and othermembrane separations can routinely require the additional and/orcombined use of a number of different techniques, thus increasing thecomplexity and expense of monitoring.

[0008] Accordingly, a need exists to monitor and/or control membraneseparation processes which can treat feed streams, such as aqueous feedstreams, suitable for use in industrial processes where conventionalmonitoring techniques are generally complex and/or may lack thesensitivity and selectivity necessary to adequately monitor one or moreprocess parameters specific to membrane separation processes which areimportant to the evaluation of the performance of membrane separation.

SUMMARY OF THE INVENTION

[0009] The first aspect of the instant claimed invention is a method formonitoring a membrane separation process comprising the steps of:

[0010] (a) providing an industrial process, wherein within saidindustrial process there are feed streams comprising one or more solutesin an aqueous liquid;

[0011] (b) providing a membrane capable of removing solutes from a feedstream by separating said feed stream into a first stream and a secondstream, wherein said first steam is the permeate stream and said secondstream is the concentrate stream;

[0012] (c) selecting an inert fluorescent tracer and a taggedfluorescent agent; wherein the selection is made such that it is knownin advance whether said inert fluorescent tracer and said taggedfluorescent agent are either

[0013] (i) capable of traveling through the membrane into the permeatestream either separately or together, or

[0014] (ii) not capable of passing through the membrane into thepermeate stream either separately or together;

[0015] (d) introducing the inert fluorescent tracer and taggedfluorescent agent into the feed stream;

[0016] (e) providing one or more fluorometers, to enable the detectionof the fluorescent signal of the inert fluorescent tracer in the feedstream and the concentrate and optionally the permeate and the detectionof the fluorescent signal of the tagged fluorescent agent in the feedstream and the concentrate and optionally the permeate;

[0017] (f) using the one or more fluorometers to detect the fluorescentsignal of the inert fluorescent tracer in the feed stream and theconcentrate and optionally the permeate and to detect the fluorescentsignal of the tagged fluorescent agent in the feed stream and theconcentrate and optionally the permeate;

[0018] (g) converting the detected fluorescent signal of the inertfluorescent tracer into the concentration of the inert fluorescenttracer and converting the detected fluorescent signal of the taggedfluorescent agent into the concentration of the tagged fluorescentagent.

[0019] The second aspect of the instant claimed invention is a methodfor detecting damage to a membrane used in a membrane separation processcomprising the steps of:

[0020] (a) providing an industrial process, wherein within saidindustrial process there are feed streams comprising one or more solutesin an aqueous liquid;

[0021] (b) providing a membrane capable of removing solutes from a feedstream by separating said feed stream into a first stream and a secondstream, wherein said first steam is the permeate stream and said secondstream is the concentrate stream;

[0022] (c) selecting an inert fluorescent tracer and a taggedfluorescent agent; wherein the selection is made such that it is knownin advance that one or both of said inert fluorescent tracer and saidtagged fluorescent agent are not capable of passing through the membraneinto the permeate stream;

[0023] (d) introducing the inert fluorescent tracer and taggedfluorescent agent into the feed stream;

[0024] (e) providing one or more fluorometers, to enable the detectionof the fluorescent signal of the inert fluorescent tracer in the feedstream and in the permeate stream and the detection of the fluorescentsignal of the tagged fluorescent agent in the feed stream and in thepermeate stream;

[0025] (f) using the one or more fluorometers to detect the fluorescentsignal of the inert fluorescent tracer in the feed stream and in thepermeate stream and to detect the fluorescent signal of the taggedfluorescent agent in the feed stream and in the permeate stream;

[0026] wherein, if one or both of the fluorescent signals of the inertfluorescent tracer and the tagged fluorescent agent are found in thepermeate then this indicates the membrane is damaged in some way.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0027] The first aspect of the instant claimed invention is a method formonitoring a membrane separation process comprising the steps of:

[0028] (a) providing an industrial process, wherein within saidindustrial process there are feed streams comprising one or more solutesin an aqueous liquid;

[0029] (b) providing a membrane capable of removing solutes from a feedstream by separating said feed stream into a first stream and a secondstream, wherein said first steam is the permeate stream and said secondstream is the concentrate stream;

[0030] (c) selecting an inert fluorescent tracer and a taggedfluorescent agent; wherein the selection is made such that it is knownin advance whether said inert fluorescent tracer and said taggedfluorescent agent are either

[0031] (i) capable of traveling through the membrane into the permeatestream either separately or together, or

[0032] (ii) not capable of passing through the membrane into thepermeate stream either separately or together;

[0033] (d) introducing the inert fluorescent tracer and taggedfluorescent agent into the feed stream;

[0034] (e) providing one or more fluorometers, to enable the detectionof the fluorescent signal of the inert fluorescent tracer in the feedstream and the concentrate and optionally the permeate and the detectionof the fluorescent signal of the tagged fluorescent agent in the feedstream and the concentrate and optionally the permeate;

[0035] (f) using the one or more fluorometers to detect the fluorescentsignal of the inert fluorescent tracer in the feed stream and theconcentrate and optionally the permeate and to detect the fluorescentsignal of the tagged fluorescent agent in the feed stream and theconcentrate and optionally the permeate;

[0036] converting the detected fluorescent signal of the inertfluorescent tracer into the concentration of the inert fluorescenttracer in the feed stream and the concentrate and optionally thepermeate and converting the detected fluorescent signal of the taggedfluorescent agent into the concentration of the tagged fluorescent agentin the feed stream and the concentrate and optionally the permeate.

[0037] The present invention is applicable to all industries that canemploy membrane separation processes. For example, the different typesof industrial processes in which the method-of the present invention canbe applied generally include raw water processes, waste water processes,industrial water processes, municipal water treatment, food and beverageprocesses, pharmaceutical processes, electronic manufacturing, utilityoperations, pulp and paper processes, mining and mineral processes,transportation-related processes, textile processes, plating and metalworking processes, laundry and cleaning processes, leather and tanningprocesses, and paint processes.

[0038] In particular, food and beverage processes can include, forexample, dairy processes relating to the production of cream, low-fatmilk, cheese, specialty milk products, protein isolates, lactosemanufacture, whey, casein, fat separation, and brine recovery fromsalting cheese. Uses relating to the beverage industry including, forexample, fruit juice clarification, concentration or deacidification,alcoholic beverage clarification, alcohol removal for low-alcoholcontent beverages, process water; and uses relating to sugar refining,vegetable protein processing, vegetable oil production/processing, wetmilling of grain, animal processing (e.g., red meat, eggs, gelatin, fishand poultry), reclamation of wash waters, food processing waste and thelike.

[0039] Examples of industrial water uses as applied to the presentinvention include, for example, boiler water production, process waterpurification and recycle/reuse, softening of raw water, treatment ofcooling water blow-down, reclamation of water from papermakingprocesses, desalination of sea and brackish water for industrial andmunicipal use, drinking/raw/surface water purification including, forexample, the use of membranes to exclude harmful micro-organisms fromdrinking water, polishing of softened water, membrane bio-reactors,mining and mineral process waters.

[0040] Examples of waste water treatment applications with respect tothe tracer monitoring of the methods of the present invention include,for example, industrial waste water treatment, biological wastetreatment systems, removal of heavy metal contaminants, polishing oftertiary effluent water, oily waste waters, transportation relatedprocesses (e.g., tank car wash water), textile waste (e.g., dye,adhesives, size, oils for wool scouring, fabric finishing oils), platingand metal working waste, laundries, printing, leather and tanning, pulpand paper (e.g., color removal, concentration of dilute spent sulfiteliquor, lignon recovery, recovery of paper coatings), chemicals (e.g.,emulsions, latex, pigments, paints, chemical reaction by-products), andmunicipal waste water treatment (e.g., sewage, industrial waste).

[0041] Other examples of industrial applications of the presentinvention include, for example, semiconductor rinse water processes,production of water for injection, pharmaceutical water including waterused in enzyme production/recovery and product formulation, andelectro-coat paint processing.

[0042] It should be appreciated that the present invention can be usedwith respect to a number of different types of membrane separationprocesses including, for example, cross-flow processes, dead-end flowprocesses, reverse osmosis, ultrafiltration, microfiltration,nanofiltration, electrodialysis, electrodeionization, pervaporation,membrane extraction, membrane distillation, membrane stripping, membraneaeration and the like or combinations thereof. Reverse osmosis,ultrafiltration, microfiltration and nanofiltration are the preferredmembrane separation processes.

[0043] In reverse osmosis, the feed stream is typically processed undercross-flow conditions. In this regard, the feed stream flowssubstantially parallel to the membrane surface such that only a portionof the feed stream diffuses through the membrane as permeate. Thecross-flow rate is routinely high in order to provide a scouring actionthat lessens membrane surface fouling. This can also decreaseconcentration polarization effects (e.g., concentration of solutes inthe reduced-turbulence boundary layer at the membrane surface which canincrease the osmotic pressure at the membrane and thus reduces permeateflow). The concentration polarization effects can inhibit the feedstream water from passing through the membrane as permeate, thusdecreasing the recovery ratio, e.g., the ratio of permeate to appliedfeed stream. A recycle loop(s) may be employed to maintain a high flowrate across the membrane surface.

[0044] Reverse osmosis processes can employ a variety of different typesof membranes. Such commercial membrane element types include, withoutlimitation, hollow fiber membrane elements, tubular membrane elements,spiral-wound membrane elements, plate and frame membrane elements, andthe like, some of which are described in more detail in “The Nalco WaterHandbook,” Second Edition, Frank N. Kemmer ed., McGraw-Hill BookCompany, New York, N.Y., 1988, particularly Chapter 15 entitled“Membrane Separation”. It should be appreciated that a single membraneelement may be used in a given membrane filtration system, but a numberof membrane elements can also be used depending on the industrialapplication.

[0045] A typical reverse osmosis system is described as an example ofmembrane filtration and more generally membrane separation. Reverseosmosis uses mainly spiral wound elements or modules, which areconstructed by winding layers of semi-porous membranes with feed spacersand permeate water carriers around a central perforated permeatecollection tube. Typically the modules are sealed with tape and/orfiberglass over-wrap. The resulting construction has one channel whichcan receive an inlet flow. The inlet stream flows longitudinally alongthe membrane module and exits the other end as a concentrate stream.Within the module, water passes through the semi-porous membrane and istrapped in a permeate channel which flows to a central collection tube.From this tube it flows out of a designated channel and is collected.

[0046] In practice, membrane modules are stacked together, end to end,with inter-connectors joining the permeate tubes of the first module tothe permeate tube of the second module, and so on. These membrane modulestacks are housed in pressure vessels. Within the pressure vessel feedwater passes into the first module in the stack, which removes a portionof the water as permeate water. The concentrate stream from the firstmembrane becomes the feed stream of the second membrane and so on downthe stack. The permeate streams from all of the membranes in the stackare collected in the joined permeate tubes. Only the feed streamentering the first module, the combined permeate stream and the finalconcentrate stream from the last module in the stack are commonlymonitored.

[0047] Within most reverse osmosis systems, pressure vessels arearranged in either “stages” or “passes.” In a staged membrane system,the combined concentrate streams from a bank of pressure vessels aredirected to a second bank of pressure vessels where they become the feedstream for the second stage. Commonly systems have 2 to 3 stages withsuccessively fewer pressure vessels in each stage. For example, a systemmay contain 4 pressure vessels in a first stage, the concentrate streamsof which feed 2 pressure vessels in a second stage, the concentratestreams of which in turn feed 1 pressure vessel in the third stage. Thisis designated as a “4:2:1” array. In a staged membrane configuration,the combined permeate streams from all pressure vessels in all stagesare collected and used without further membrane treatment. Multi-stagesystems are used when large volumes of purified water are required, forexample for boiler feed water. The permeate streams from the membranesystem may be further purified by ion exchange or other means.

[0048] In a multi-pass system, the permeate streams from each bank ofpressure vessels are collected and used as the feed to the subsequentbanks of pressure vessels. The concentrate streams from all pressurevessels are combined without further membrane treatment of eachindividual stream. Multi-pass systems are used when very high puritywater is required, for example in the microelectronics or pharmaceuticalindustries.

[0049] It should be clear from the above examples that the concentratestream of one stage of an RO system can be the feed stream of anotherstage. Likewise the permeate stream of a single pass of a multi-passsystem may be the feed stream of a subsequent pass. A challenge inmonitoring systems such as the reverse osmosis examples cited above isthat there are a limited number of places where sampling and monitoringcan occur, namely the feed, permeate and concentrate streams. In some,but not all, systems “inter-stage” sampling points allowsampling/monitoring of the first stage concentrate/second stage feedstream. Similar inter-pass sample points may be available on multi-passsystems as well.

[0050] In practice it is possible to “probe” the permeate collectiontube within a single pressure vessel to sample the quality of thepermeate from each of the membrane elements in the stack. It is a timeconsuming, messy and inexact method and is not routinely applied exceptin troubleshooting situations. There is no currently accepted method ofexamining the feed/concentrate stream quality of individual membraneelements within a single pressure vessel.

[0051] In contrast to cross-flow filtration membrane separationprocesses, conventional filtration of suspended solids can be conductedby passing a feed fluid through a filter media or membrane in asubstantially perpendicular direction. This effectively creates one exitstream during the service cycle. Periodically, the filter is backwashedby passing a clean fluid in a direction opposite to the feed, generatinga backwash effluent containing species that have been retained by thefilter. Thus conventional filtration produces a feed stream, a purifiedstream and a backwash stream. This type of membrane separation istypically referred to as dead-end flow separation and is typicallylimited to the separation of suspended particles greater than about onemicron in size.

[0052] Cross-flow filtration techniques, on the other hand, can be usedfor removing smaller particles (generally about one micron in size orless), colloids and dissolved solutes. Such types of cross-flow membraneseparation systems can include, for example, reverse osmosis,microfiltration, ultrafiltration, nanofiltration, electrodialysis or thelike. Reverse osmosis can remove even low molecular weight dissolvedspecies that are at least about 0.0001 to about 0.001 microns in minimumdiameter, including, for example, ionic and nonionic species, lowmolecular weight molecules, water-soluble macromolecules or polymers,suspended solids, colloids, and such substances as bacteria and viruses.

[0053] In this regard, reverse osmosis is often used commercially totreat water that has a moderate to high (e.g., 500 ppm or greater) totaldissolved solids (“TDS”) content. Typically on order of from about 2percent to about 5 percent of the TDS of a feed stream will pass throughthe membrane. Thus, in general the permeate may not be entirely free ofsolutes. In this regard, the TDS of reverse osmosis permeates may be toohigh for some industrial applications, such as use as makeup water forhigh pressure boilers. Therefore, reverse osmosis systems and other likemembrane separation systems are frequently used prior to and incombination with an ion exchange process or other suitable process toreduce the TDS loading on the resin and to decrease the amount ofhazardous material used and stored for resin regeneration, such as acidsand sodium hydroxide.

[0054] As discussed above, the performance of membrane separationsystems can vary with respect to a number of different operationalconditions specific to membrane separation, such as temperature, pH,pressure, permeate flow, activity of treatment and/or cleaning agents,fouling activity and the like. When developing and/or implementing amonitoring and/or control program based on the detection of fluorescentagents (e.g., inert fluorescent tracers and tagged fluorescent agents),the effects of the operational conditions specific to membraneseparation must necessarily be taken into consideration. As previouslydiscussed, the operational conditions of water treatment processes canvary greatly from process to process. In this regard, the monitoringtechniques as applied to each process can also vary greatly.

[0055] Membrane separation processes and the monitoring thereof areunique because of the following considerations.

[0056] 1. Systems are constructed with limited flexibility in terms ofwhere monitoring may be done and/or where samples may be collected.

[0057] 2. Membrane separation systems include a concentrationpolarization layer that forms as water is permeated through the barrier.This is not present in other water treatment systems, such as coolingwater systems.

[0058] 3. Membrane separation systems operate at significantly lowertemperatures than industrial processes where inverse solubility ofsolutes is a problem. However, in the case of membrane separationsystems such as reverse osmosis and nanofiltration, this low temperatureleads to scaling from salts that are less likely to be problematic inhigher temperature processes (such as silica and silicate salts). Inthis regard, typical day-to-day membrane separation operations (forexample RO and NF) occur at about 75° F.

[0059] 4. Because it is essential that the surface of the membraneremain clean, a relatively small amount of fine precipitate can cause asignificant performance loss. The performance loss in a membrane is,thus, more sensitive to precipitate deposition as compared to coolingwater treatment. In this regard, performance loss in a membrane canoccur at a film thickness appreciably lower than that required for heattransfer loss to occur in a cooling water system.

[0060] 5. Water loss in membrane filtration is due to “permeation” orpassage through the membrane barrier. Damaged or otherwise imperfectmembranes are susceptible to undesirable leakage of solutes through themembrane. Thus it is critical to monitor leakage through the membrane tokeep it operating at maximum efficiency.

[0061] 6. The thin, semi-permeable films (polymeric, organic orinorganic) are sensitive to degradation by chemical species. Productswhich contact the membrane surface must be compatible with the membranechemistry to avoid damaging the surface and thereby degradingperformance.

[0062] 7. Chemical treatments used in membrane systems must bedemonstrated to be compatible with the membrane material prior to use.Damage from incompatible chemicals can result in immediate loss ofperformance and perhaps degradation of the membrane surface. Suchimmediate, irreversible damage from a chemical treatment is highlyuncommon in cooling water systems.

[0063] Based on these differences, a number of different factors andconsiderations must necessarily be taken into account when developingand/or implementing monitoring and/or controlling programs with respectto membrane separation systems as compared to other water treatmentprocesses, such as cooling water treatment processes.

[0064] A variety of different and suitable types of compounds can beused as inert fluorescent tracers. The term “inert,” as used hereinrefers to an inert fluorescent tracer that is not appreciably orsignificantly affected by any other chemistry in the system, or by theother system parameters such as pH, temperature, ionic strength, redoxpotential, microbiological activity or biocide concentration. Toquantify what is meant by “not appreciably or significantly affected”,this statement means that an inert fluorescent compound has no more thana 10% change in its fluorescent signal, under severe conditionsencountered in industrial water systems. Severe conditions normallyencountered in industrial water systems are known to people of ordinaryskill in the art of industrial water systems.

[0065] In an embodiment, the inert fluorescent compounds can include,for example, the following compounds:

[0066] 3,6-acridinediamine, N,N,N′,N′-tetramethyl-, monohydrochloride,also known as Acridine Orange (CAS Registry No. 65-61-2),

[0067] 2-anthracenesulfonic acid sodium salt (CAS Registry No.16106-40-4),

[0068] 1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) andsalts thereof,

[0069] 2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) andsalts thereof,

[0070] 1,8-anthracenedisulfonic acid (CAS Registry No. 61736-92-3) andsalts thereof,

[0071] anthra[9,1,2-cde]benzo[rst]pentaphene-5,10-diol,16,17-dimethoxy-, bis(hydrogen sulfate), disodium salt, also known asAnthrasol Green IBA (CAS Registry No. 2538-84-3, aka Solubilized VatDye),

[0072] bathophenanthrolinedisulfonic acid disodium salt (CAS RegistryNo. 52746-49-3),

[0073] amino 2,5-benzene disulfonic acid (CAS Registry No. 41184-20-7),

[0074] 2-(4-aminophenyl)-6-methylbenzothiazole (CAS Registry No.92-36-4),

[0075] 1H-benz[de]isoquinoline-5-sulfonic acid,6-amino-2,3-dihydro-2-(4-methylphenyl)-1,3-dioxo-, monosodium salt, alsoknown as Brilliant Acid Yellow 8G (CAS Registry No. 2391-30-2, akaLissamine Yellow FF, Acid Yellow 7),

[0076] phenoxazin-5-ium,1-(aminocarbonyl)-7-(diethylamino)-3,4-dihydroxy-, chloride, also knownas Celestine Blue (CAS Registry No. 1562-90-9),

[0077] benzo[a]phenoxazin-7-ium, 5,9-diamino-, acetate, also known ascresyl violet acetate (CAS Registry No. 10510-54-0),

[0078] 4-dibenzofuransulfonic acid (CAS Registry No. 42137-76-8),

[0079] 3-dibenzoftiransulfonic acid (CAS Registry No. 215189-98-3),

[0080] 1-ethylquinaldinium iodide (CAS Registry No. 606-53-3),

[0081] fluorescein (CAS Registry No. 2321-07-5),

[0082] fluorescein, sodium salt (CAS Registry No. 518-47-8, aka AcidYellow 73, Uranine),

[0083] Keyfluor White ST (CAS Registry No. 144470-48-4, aka Flu. Bright28),

[0084] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt, also known as Keyfluor White CN (CAS Registry No.16470-24-9),

[0085] C.I. Fluorescent Brightener 230, also known as Leucophor BSB (CASRegistry No. 68444-86-0),

[0086] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt, also known as Leucophor BMB (CAS Registry No.16470-24-9, aka Leucophor U, Flu. Bright. 290),

[0087] 9,9′-biacridinium, 10,10′-dimethyl-, dinitrate, also known asLucigenin (CAS Registry No. 2315-97-1, aka bis-N-methylacridiniumnitrate),

[0088]1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol,also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5),

[0089] mono-, di-, or tri-sulfonated napthalenes, including but notlimited to

[0090] 1,5-naphthalenedisulfonic acid, disodium salt (hydrate) (CASRegistry No. 1655-29-4, aka 1,5-NDSA hydrate),

[0091] 2-amino-1-naphthalenesulfonic acid (CAS Registry No. 81-16-3),

[0092] 5-amino-2-naphthalenesulfonic acid (CAS Registry No. 119-79-9),

[0093] 4-amino-3-hydroxy-1-naphthalenesulfonic acid (CAS Registry No.90-51-7),

[0094] 6-amino-4-hydroxy-2-naphthalenesulfonic acid (CAS Registry No.116-63-2),

[0095] 7-amino-1,3-naphthalenesulfonic acid, potassium salt (CASRegistry No. 79873-35-1),

[0096] 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid (CAS RegistryNo. 90-20-0),

[0097] 5-dimethylamino-1-naphthalenesulfonic acid (CAS Registry No.4272-77-9),

[0098] 1-amino-4-naphthalene sulfonic acid (CAS Registry No. 84-86-6),

[0099] 1-amino-7-naphthalene sulfonic acid (CAS Registry No. 119-28-8),and

[0100] 2,6-naphthalenedicarboxylic acid, dipotassium salt (CAS RegistryNo. 2666-06-0),

[0101] 3,4,9,10-perylenetetracarboxylic acid (CAS Registry No. 81-32-3),

[0102] C.I. Fluorescent Brightener 191, also known as Phorwite CL (CASRegistry No. 12270-53-0),

[0103] C.I. Fluorescent Brightener 200, also known as Phorwite BKL (CASRegistry No. 61968-72-7),

[0104] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-,dipotassium salt, also known as Phorwite BHC 766 (CAS Registry No.52237-03-3),

[0105] benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt,also known as Pylaklor White S-15A (CAS Registry No. 6416-68-8),

[0106] 1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt (CAS RegistryNo. 59572-10-0), pyranine, (CAS Registry No. 6358-69-6, aka8-hydroxy-1,3,6-pyrenetrisulfonic acid, trisodium salt),

[0107] quinoline (CAS Registry No. 91-22-5),

[0108] 3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide, also known as Rhodalux(CAS Registry No. 550-82-3),

[0109] xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-,chloride, disodium salt, also known as Rhodamine WT (CAS Registry No.37299-86-8),

[0110] phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride, alsoknown as Safranine 0 (CAS Registry No. 477-73-6),

[0111] C.I. Fluorescent Brightener 235, also known as Sandoz CW (CASRegistry No. 56509-06-9),

[0112] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt, also known as Sandoz CD (CAS Registry No. 16470-24-9,aka Flu. Bright. 220),

[0113] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt, also known as Sandoz TH-40 (CAS Registry No. 32694-95-4),

[0114] xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, innersalt, sodium salt, also known as Sulforhodamine B (CAS Registry No.3520-42-1, aka Acid Red 52),

[0115] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt, also known as Tinopal 5BM-GX (CAS Registry No.169762-28-1),

[0116] Tinopol DCS (CAS Registry No. 205265-33-4),

[0117] benzenesulfonic acid,2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis-, disodium saltalso known as Tinopal CBS-X (CAS Registry No. 27344-41-8),

[0118] benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt,also known as Tinopal RBS 200, (CAS Registry No. 6416-68-8),

[0119] 7-benzothiazolesulfonic acid,2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt,also known as Titan Yellow (CAS Registry No. 1829-00-1, aka ThiazoleYellow G), and all ammonium, potassium and sodium salts thereof, and alllike agents and suitable mixtures thereof.

[0120] Preferred inert fluorescent tracers include:

[0121]1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol,also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5),

[0122] fluorescein (CAS Registry No. 2321-07-5),

[0123] fluorescein, sodium salt (CAS Registry No. 518-47-8, aka AcidYellow 73, Uranine),

[0124] 2-anthracenesulfonic acid sodium salt (CAS Registry No.16106-40-4),

[0125] 1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) andsalts thereof,

[0126] 2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) andsalts thereof,

[0127] 1,8-anthracenedisulfonic acid (CAS Registry No. 61736-92-3) andsalts thereof,

[0128] mono-, di-, or tri-sulfonated napthalenes, including but notlimited to

[0129] 1,5-naphthalenedisulfonic acid, disodium salt (hydrate) (CASRegistry No. 1655-29-4, aka 1,5-NDSA hydrate),

[0130] 2-amino-1-naphthalenesulfonic acid (CAS Registry No. 81-16-3),

[0131] 5-amino-2-naphthalenesulfonic acid (CAS Registry No. 119-79-9),

[0132] 4-amino-3-hydroxy-1-naphthalenesulfonic acid (CAS Registry No.90-51-7),

[0133] 6-amino-4-hydroxy-2-naphthalenesulfonic acid (CAS Registry No.116-63-2),

[0134] 7-amino-1,3-naphthalenesulfonic acid, potassium salt (CASRegistry No. 79873-35-1),

[0135] 4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid (CAS RegistryNo. 90-20-0),

[0136] 5-dimethylamino-1-naphthalenesulfonic acid (CAS Registry No.4272-77-9),

[0137] 1-amino-4-naphthalene sulfonic acid (CAS Registry No. 84-86-6),

[0138] 1-amino-7-naphthalene sulfonic acid (CAS Registry No. 119-28-8),and

[0139] 2,6-naphthalenedicarboxylic acid, dipotassium salt (CAS RegistryNo. 2666-06-0),

[0140] 3,4,9,10-perylenetetracarboxylic acid (CAS Registry No. 81-32-3),

[0141] C.I. Fluorescent Brightener 191, also known as, Phorwite CL (CASRegistry No. 12270-53-0),

[0142] C.I. Fluorescent Brightener 200, also known as Phorwite BKL (CASRegistry No. 61968-72-7),

[0143] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-,dipotassium salt, also known as Phorwite BHC 766 (CAS Registry No.52237-03-3),

[0144] benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt,also known as Pylaklor White S-1SA (CAS Registry No. 6416-68-8),

[0145] 1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt (CAS RegistryNo. 59572-10-0),

[0146] pyranine, (CAS Registry No. 6358-69-6, aka8-hydroxy-1,3,6-pyrenetrisulfonic acid, trisodium salt),

[0147] quinoline (CAS Registry No. 91-22-5),

[0148] 3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide, also known as Rhodalux(CAS Registry No. 550-82-3),

[0149] xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-,chloride, disodium salt, also known as Rhodamine WT (CAS Registry No.37299-86-8),

[0150] phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride, alsoknown as Safranine O (CAS Registry No. 477-73-6),

[0151] C.I. Fluorescent Brightener 235, also known as Sandoz CW (CASRegistry No. 56509-06-9),

[0152] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt, also known as Sandoz CD (CAS Registry No. 16470-24-9,aka Flu. Bright. 220),

[0153] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt, also known as Sandoz TH-40 (CAS Registry No. 32694-95-4),

[0154] xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-, innersalt, sodium salt, also known as Sulforhodamine B (CAS Registry No.3520-42-1, aka Acid Red 52),

[0155] benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt, also known as Tinopal 5BM-GX (CAS Registry No.169762-28-1),

[0156] Tinopol DCS (CAS Registry No. 205265-33-4),

[0157] benzenesulfonic acid,2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis-, disodium salt,also known as Tinopal CBS-X (CAS Registry No. 27344-41-8),

[0158] benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt,also known as Tinopal RBS 200, (CAS Registry No. 6416-68-8),

[0159] 7-benzothiazolesulfonic acid,2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt,also known as Titan Yellow (CAS Registry No. 1829-00-1, aka ThiazoleYellow G), and all ammonium, potassium and sodium salts thereof, and alllike agents and suitable mixtures thereof.

[0160] The most preferred inert fluorescent tracers of the presentinvention include 1,3,6,8-pyrenetetrasulfonic acid tetrasodium salt (CASRegistry No. 59572-10-0); 1,5-naphthalenedisulfonic acid disodium salt(hydrate) (CAS Registry No. 1655-29-4, aka 1,5-NDSA hydrate);xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride,disodium salt, also known as Rhodamine WT (CAS Registry No. 37299-86-8);1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-D-ribitol,also known as Riboflavin or Vitamin B2 (CAS Registry No. 83-88-5);fluorescein (CAS Registry No. 2321-07-5); fluorescein, sodium salt (CASRegistry No. 518-47-8, aka Acid Yellow 73, Uranine);2-anthracenesulfonic acid sodium salt (CAS Registry No. 16106-40-4);1,5-anthracenedisulfonic acid (CAS Registry No. 61736-91-2) and saltsthereof; 2,6-anthracenedisulfonic acid (CAS Registry No. 61736-95-6) andsalts thereof; 1,8-anthracenedisulfonic acid (CAS Registry No.61736-92-3) and salts thereof; and mixtures thereof. The fluorescenttracers listed above are commercially available from a variety ofdifferent chemical supply companies.

[0161] In addition to the tracers listed above, those skilled in the artwill recognize that salts using alternate counter ions may also be used.Thus, for example, anionic tracers which have Na⁺ as a counter ion couldalso be used in forms where the counter ion is chosen from the list of:K⁺, Li⁺, NH₄ ⁺, Ca⁺², Mg⁺² or other appropriate counter ions. In thesame way, cationic tracers may have a variety of counter ions, forexample: Cl⁻, So₄ ⁻², PO₄ ⁻³, HPO₄ ⁻²; H₂PO₄ ⁻; CO₃ ⁻²; HCO₃ ⁻; or otherappropriate counter ions.

[0162] Modifications of these tracers to control molecular weight orphysical size within a desirable size range by, for example, affixingthem to an inert polymeric molecule, incorporating them into afluorescent microsphere or adding additional chemical moieties in theside chains of the molecules should be obvious to those skilled in theart. Such modifications are included herein.

[0163] The inert fluorescent tracer is used in combination with thetagged fluorescent agent to enhance monitoring of membrane separation,particularly with respect to the monitoring and effect of treatmentagents added to membrane separation in order to treat scaling and/orfouling.

[0164] In this regard, the inert fluorescent tracer and the taggedfluorescent agent can each be measured such that fluctuations in theratio of the inert fluorescent tracer to the tagged fluorescent agentcan be monitored. Such fluctuations can be used to signal consumption ofa chemical treatment agent, the onset of scaling and/or fouling, or thelike. Adjustments to membrane separation can then be made controllablyand responsively to correct for fluctuations with respect to the ratio.Thus, membrane separation performance can be enhanced by, for example,adjusting the amount of treatment agents added to optimize the treatmentof scale, foulants and other like deposits which can adversely impactmembrane separation.

[0165] The fluorescent compounds of the present invention (i.e. theinert fluorescent tracer, the tagged fluorescent agent, or combinationsthereof) can be added to the membrane separation process in any suitableform. For example, the present invention uses a combination of inertfluorescent tracers and tagged fluorescent agents. In this regard, theinert fluorescent tracers can be used to monitor the dosage of treatmentagents (e.g., anti-scalants and/or biocides) that are added to theprocess. The tagged fluorescent agents can be used to monitor the activechemical ingredient of such treatment. Thus, the loss of treatment dueto, for example, adsorption of a treatment agent on a growing crystal,can be detected based on fluctuations in the ratio of inert fluorescenttracer(s) to tagged fluorescent agents during membrane separating. Thediagnostic capabilities of the present invention can be performed with ahigh degree of sensitivity, selectivity and accuracy with respect to themonitoring of process parameters specific to a membrane separation. Inthis regard, the method and system of the present invention can beeffectively used to optimize the performance of membrane separationprocesses.

[0166] The tagged fluorescent agent can include a variety of differentand suitable materials. In an embodiment, the tagged fluorescent agentincludes a polymeric compound that has one or more fluorescent groupsattached or incorporated to its polymeric structure. In an embodiment,the polymeric compound has a molecular weight that ranges from about2000 atomic mass units (“amu”) to about 20,000 amu. The polymericcompound is water-soluble and has one or more monomer components in anysuitable amount including, for example, acrylamide, acrylic acid,methacrylamide, vinyl acetate, dimethylaminoethyl acrylate methylchloride quaternary salt, dimethylaminoethyl acrylate benzyl chloridequaternary salt, diallyldimethyl ammonium chloride, N-vinyl formamide,dimethylaminoethyl methacrylate methyl chloride quaternary salt,dimethylaminoethyl methacrylate benzyl chloride quaternary salt,methacrylamino propyl trimethyl ammonium chloride, acrylamidopropyltrimethyl ammonium chloride, and combinations thereof. Differentcombinations of these polymeric compounds may be chosen for theirability to target specific scales.

[0167] The fluorescent group of the tagged fluorescent agent can includea variety of different and suitable materials including, hydroxyallyloxypropyl napthalimide quat,4-methoxy-N-(3-N′N′-dimethylaminopropyl)napthalimide,2-hydroxy-3-allyloxypropyl quat, 8-(3-vinylbenzyloxy)-1,3,6-pyrenetrisulfonic acid, 8-(4-vinylbenzyloxy)-1,3,6-pyrene trisulfonic acid,8-(allyloxy)-1,3,6-pyrene trisulfonic acid, 1-(substituted)naphthalene,9-(substituted) anthracene, 2-(substituted) quinoline monohydrochloride,2-(substituted) benzimidazole, 5-(substituted) fluorescein,4-(substituted)coumarin, coumarin derivatives,3-(substituted)-6,7-dimethoxy-1-methyl-2(1H)-quinoxazolinone, mixturesthereof and derivatives thereof.

[0168] In an embodiment, the tagged fluorescent agent of the presentinvention includes a hydroxy allyloxy propyl naphthalimide quat, such as4-methoxy-N-(3-N′,N′-dimethylaminopropyl)napthalimide,2-hydroxy-3-allyloxy propyl quat, tagged onto a 35% aqueous solution ofa sulfomethylated copolymer of acrylate and acrylamide wherein thefluorescent group is an amount of about 2% or less by weight of thepolymeric compound. A variety of different and suitable taggedfluorescent agents are disclosed in the U.S. Pat. Nos. 5,128,419;5,171,450; 5,216,086; 5,260,386 and 5,986,030 which are each hereinincorporated by reference. In an embodiment, the tagged fluorescentagent or moiety is stable at a pH ranging from about 2 to about 10.

[0169] It should be appreciated that a variety of different and suitablemodifications, variations and/or derivatives thereof of theabove-described tagged fluorescent agents and/or fluorescent groups canbe used. For example, the hydrogen of the sulfonic acid groups of thesubstituted pyrene trisulfonic acids discussed above can be replacedwith a suitable metal ion including, for example, sodium, potassium,cesium, rubidium, lithium and ammonium. Further, the allyloxy group ofthe substituted pyrene sulfonic acid can include any suitable number ofcarbon atoms including, for example, three, four, five, six, eight,eleven and the like.

[0170] The selection of inert fluorescent tracer and tagged fluorescentagent is made based on the membrane system being monitored and thepurpose of the monitoring. Factors influencing the permeability of amaterial through a membrane include the following:

[0171] a) Size of the material and size of the holes in the membrane;

[0172] b) Charge of the material and charge (or lack thereof) of themembrane;

[0173] c) Tendency of the material to adsorb on the surface of themembrane, rather than pass through the membrane;

[0174] d) Concentration Differentials between the material on one sideof the membrane and the material on the other side of the membrane; and

[0175] e) Residence times of the feed stream containing the materialbeing in contact with the membrane.

[0176] Persons of ordinary skill in the art of membranes know how to setup and run the routine tests necessary to determine whether a particularinert tracer in combination with a particular tagged fluorescent agentis capable of passing through the holes in a membrane.

[0177] It should be appreciated that the amount of inert fluorescenttracer and tagged fluorescent agent to be added to the membraneseparation process that is effective without being grossly excessivewill vary with a respect to a variety of factors including, withoutlimitation, the monitoring method selected, the extent of backgroundinterference associated with the selected monitoring method, themagnitude of the expected tracer(s) concentration in the feedwaterand/or concentrate, the monitoring mode (such as an on-line continuousmonitoring mode), and other similar factors. In an embodiment, thedosage of each of an inert fluorescent tracer(s) and tagged fluorescentagent to the feed water of the membrane separation system includes anamount that is at least sufficient to provide a measurable concentrationof the fluorescent agents (i.e., inert fluorescent tracer and taggedfluorescent agent) in the concentrate at steady state of at least about5 ppt, and preferably at least about 1 part per billion (“ppb”) or about5 ppb or higher, such as, up to about 100 ppm or about 200 ppm, or evenas high as about 1000 ppm in the concentrate or other effluent stream.In an embodiment, the amount of fluorescent agents ranges from about 5ppt to about 1000 ppm, preferably from about 1 ppb to about 50 ppm, andmore preferably from about 5 ppb to about 50 ppb.

[0178] It should be appreciated that the concentration of taggedfluorescent agent can be modified by varying the number of fluorescentgroups on the polymeric compound and/or varying the concentration of thepolymeric compound.

[0179] The inert fluorescent tracers and tagged fluorescent agents ofthe present invention can be detected by using a variety of differentand suitable fluorometers. For example, fluorescence emissionspectroscopy on a substantially continuous basis, at least over a giventime period, is one of the preferred analytical techniques according toan embodiment of the present invention. One method for the continuouson-stream measuring of chemical species by fluorescence emissionspectroscopy and other analysis methods is described in U.S. Pat. No.4,992,380, B. E. Moriarty, J. J. Hickey, W. H. Hoy, J. E. Hoots and D.A. Johnson, issued Feb. 12, 1991, incorporated hereinto by reference.

[0180] In general, for most fluorescence emission spectroscopy methodshaving a reasonable degree of practicality, it is preferable to performthe analysis without isolating in any manner the fluorescent species.Thus, there may be some degree of background fluorescence in theinfluent/feedwater and/or concentrate on which the fluorescence analysisis conducted. This background fluorescence may come from chemicalcompounds in the membrane separation system (including theinfluent/feedwater system thereof) that are unrelated to the membraneseparation process of the present invention.

[0181] In instances where the background fluorescence is low, therelative measurable intensities (measured against a standard fluorescentcompound at a standard concentration and assigned a relative intensity,for instance 100) of the fluorescence of each of the tracer and thetagged fluorophore versus the background can be very high, for instancea ratio of 100/10 or 500/10, when certain combinations of excitation andemission wavelengths are employed even at low fluorescent compoundconcentrations. Such ratios would be representative of a “relativefluorescence” (under like conditions) of respectively 10 and 50. In anembodiment, the excitation/emission wavelengths and/or the amount ofeach of the tracer and tagged fluorophore employed are selected toprovide a relative fluorescence of at least about 5 or 10 for the givenbackground fluorescence anticipated.

[0182] Examples of fluorometers that may be used in the practice of thisinvention include the TRASAR® 3000 and TRASAR® 8000 fluorometers(available from Ondeo Nalco Company of Naperville, Ill.); the HitachiF-4500 fluorometer (available from Hitachi through Hitachi InstrumentsInc. of San Jose, Calif.); the JOBIN YVON FluoroMax-3 “SPEX” fluorometer(available from JOBIN YVON Inc. of Edison, N.J.); and the GilfordFluoro-IV spectrophotometer or the SFM 25 (available from Bio-techKontron through Research Instruments International of San Diego,Calif.). It should be appreciated that the fluorometer list is notcomprehensive and is intended only to show examples of fluorometers.Other commercially available fluorometers and modifications thereof canalso be used in this invention.

[0183] After the fluorometers have been selected the locations formonitoring are selected. As previously indicated, the fluorescentsignals of the inert fluorescent tracer and tagged fluorescent agent maybe detected in the feed stream, the condensate and optionally thepermeate. The detection in the permeate is optional, simply because itis known that not all the inert tracers and tagged fluorescent agentslisted herein are capable of traveling through the holes in all themembrane separation systems listed herein. It is the selection of theinert fluorescent tracer and the tagged fluorescent agent and themembrane system they are being used in that determines whether both oreither of the inert fluorescent tracer and the tagged fluorescent agentare capable of being detected in the permeate.

[0184] It should be appreciated that locations for monitoring should notbe positioned across a flow-through site that has a high concentrationof solids, for instance a solids concentration of at least about 5 orabout 10 weight percent per unit volume based on a measured volume unitof about one cubic inch. Such high solids concentration flow-throughsites are found at the site of filter cakes and the like. In thisregard, these sites may absorb, or selectively absorb, at least someamount of the tracer. This can distort the significance of monitoringcomparison. When a tracer is added upstream of, for instance, acartridge filter, in an embodiment, the monitoring location shouldpreferably be downstream of such sites.

[0185] After the fluorometer has been used to detect the fluorescentsignal of the inert fluorescent tracer and the tagged fluorescent agent,then it is possible, using techniques known to people in the art offluorometry to convert the detected fluorescent signal of the inertfluorescent tracer into the concentration of the inert fluorescenttracer in each of the streams it was detected in and to convert thedetected fluorescent signal of the tagged fluorescent agent into theconcentration of the tagged fluorescent agent in each of the streams itwas measured in.

[0186] After the concentrations of the inert fluorescent tracer andtagged fluorescent agent are known in each of the streams, then it ispossible to calculate a ratio of the concentrations. In continuousmonitoring of the system, this ratio calculation can be used todetermine useful information regarding permeation and consumption ratesin each of the streams so monitored.

[0187] The second aspect of the instant claimed invention involvesdeliberately selecting an inert tracer and a tagged fluorescent agentthat are known to not be capable of traveling through the membrane intothe permeate. Upon beginning this method, one or more fluorometers,previously described, is(are) set up to look for the fluorescent signalsof both the inert fluorescent tracer and the tagged fluorescent agent inthe permeate. Should those fluorescent signals be detected, then it isan indication that the membrane is damaged in some way, indicating theneed for inspection and maintenance.

[0188] As previously discussed, the present invention can provide highlyselective and/or sensitive monitoring of a variety of process parametersunique and specific to the membrane separation process. The monitoringis based on the measurable amounts of an inert fluorescent tracer incombination with a tagged fluorescent agent analyzed during the membraneseparation process. In this regard, the fluorescent species (i.e., inertfluorescent tracer and tagged fluorescent agent) can be detected at anysuitable location or locations within the membrane separation process,such as any suitable position in a membrane filtration process along thefeedwater stream, the concentrate stream and optionally in the permeatestream, the like or combinations thereof. This effectively correspondsto a concentration of the fluorescent species in each stream.

[0189] In this regard, monitoring of an amount of the inert fluorescenttracer and tagged fluorescent agent as it may vary during membranefiltration can be used to evaluate a number of process parametersspecific to membrane filtration such as the ratio of the inertfluorescent tracer to the tagged fluorescent agent or the like, with ahigh degree of sensitivity, selectivity and accuracy, as previouslydiscussed. The ability to evaluate these types of membrane separationprocess parameters with such level of certainty, sensitivity andselectivity and on a continual basis in accordance with the presentinvention can provide a better understanding, in real time, of theperformance of the membrane. Thus, adjustments to the membraneseparation process can be made more responsively and effectively basedon the measured amount of the inert fluorescent tracer and/or the taggedfluorescent agent, if needed, to optimize membrane performance. Forexample, adjustments can be made to increase the recovery ratio orpercent recovery of the membrane separation system. In this regard,increasing the recovery ratio or percent recovery, for unit product,will reduce the feedwater required and thus reduce feedwater costs,lower influent fluid pretreatment costs and chemical treatmentrequirements. It should be appreciated that the optimal percentrejection value can vary with respect to the type of membrane separationsystem.

[0190] Applicants have uniquely discovered that the monitoring and/orcontrolling techniques of membrane separation processes in accordancewith the present invention are faster, more sensitive, morecomprehensive and/or more reliable than conventional techniquespresently available, particularly where the monitoring methods of thepresent invention are employed on a substantially continuous basis. Thepresent invention has enhanced diagnostic capabilities such that, forexample, lack of chemical treatment, scaling and/or fouling problemsunique to membrane separation and consumption of active chemicaltreatment can be detected with reasonable certainty, with far greatersensitivity, under a far less elapsed time than the presently availablemethods. In this regard, temporary system upsets or other short-livedvariations can be detected during continuous monitoring as the transientconditions that they are, rather than as incorrect warning signs asdetected by sporadic monitoring.

[0191] The following example is presented to be illustrative of thepresent invention and to teach one of ordinary skill how to make and usethe invention. This example is not intended to limit the invention orits protection in any way.

EXAMPLE

[0192] A product is made by combining an inert tracer with a taggedfluorescent agent as follows: Soft water about 8.6 weight % Inert Tracer= about 2.0 weight % 1, 3, 6, 8 Pyrene tetrasulfonic acid, tetra sodiumsalt Poly Succinic Oligomer about 32.3 weight % Tagged fluorescent Agent= About 57.1 weight % Tagged High Stress Polymer

[0193] All of these ingredients are available from Ondeo Nalco Company,1601 W. Diehl Road, Naperville, Ill. 60563, (630) 305-1000.

[0194] The above product is put into an operating Reverse Osmosis unitas part of a chemical treatment. The material is placed in the feedstream, then two fluorometers are used to detect the fluorescent signalof the material in the feed stream and in the concentrate stream feedstream).

[0195] The polymeric component (the tagged HSP “high stress polymer” amember of the PRISM polymer family available from Ondeo Nalco Company)is expected to be consumed as it attaches to scale which is forming inthe system. By detecting the fluorescent signal of both the inerttracer, which should reflect concentration effects of the RO but notconsumption of the active ingredient, and the tagged polymer,functioning as an active scale control ingredient, it is possible todetermine the consumption of the active dispersant polymer.

[0196] In Reverse Osmosis membranes, based on knowledge of the size ofthe tagged polymer and size of the holes in the membrane; the charge ofthe tagged polymer and charge (or lack thereof) of the membrane; thetendency of the tagged polymer to adsorb on the surface of the membrane,rather than pass through the membrane; the concentration differentialsbetween the tagged polymer on one side of the membrane and the taggedpolymer on the other side of the membrane; and the residence times ofthe feed stream containing the tagged polymer being in contact with themembrane, the tagged polymer is not expected to pass through the systeminto the permeate unless there is a catastrophic membrane failure. Anexample of catastrophic failure would be a glue line tearing or openingwhich allows all components in the feed/concentrate stream to pass intothe permeate stream. Therefore, as time passes, periodicallyfluorometers are used to detect the fluorescent signals of the inerttracer and the tagged polymer in the permeate. If either the inertfluorescent tracer or the tagged polymer is detected in the permeate,then a catastrophic failure of the membrane is indicated.

[0197] While the present invention is described above in connection withpreferred or illustrative embodiments, these embodiments are notintended to be exhaustive or limiting of the invention. Rather, theinvention is intended to cover all alternatives, modifications andequivalents included within its spirit and scope, as defined by theappended claims.

1. A method for monitoring a membrane separation process comprising thesteps of: (a) providing an industrial process, wherein within saidindustrial process there are feed streams comprising one or more solutesin an aqueous liquid; (b) providing a membrane capable of removingsolutes from a feed stream by separating said feed stream into a firststream and a second stream, wherein said first steam is the permeatestream and said second stream is the concentrate stream; (c) selectingan inert fluorescent tracer and a tagged fluorescent agent; wherein theselection is made such that it is known in advance whether said inertfluorescent tracer and said tagged fluorescent agent are either (i)capable of traveling through the membrane into the permeate streameither separately or together, or (iii) not capable of passing throughthe membrane into the permeate stream either separately or together; (d)introducing the inert fluorescent tracer and tagged fluorescent agentinto the feed stream; (e) providing one or more fluorometers, to enablethe detection of the fluorescent signal of the inert fluorescent tracerin the feed stream and the concentrate and optionally the permeate andthe detection of the fluorescent signal of the tagged fluorescent agentin the feed stream and the concentrate and optionally the permeate; (f)using the one or more fluorometers to detect the fluorescent signal ofthe inert fluorescent tracer in the feed stream and the concentrate andoptionally the permeate and to detect the fluorescent signal of thetagged fluorescent agent in the feed stream and the concentrate andoptionally the permeate; (g) converting the detected fluorescent signalof the inert fluorescent tracer into the concentration of the inertfluorescent tracer in the feed stream and the concentrate and optionallythe permeate and converting the detected fluorescent signal of thetagged fluorescent agent into the concentration of the taggedfluorescent agent in the feed stream and the concentrate and optionallythe permeate.
 2. The method of claim 1 further comprising the step of(h) evaluating at least one process parameter specific to the membraneseparation process based on the amount of the inert fluorescent tracerand the tagged fluorescent agent that are measured.
 3. The method ofclaim 1 wherein the membrane separation process is selected from thegroup consisting of a cross-flow membrane separation process and adead-end flow membrane separation process.
 4. The method of claim 3wherein the membrane separation process is selected from the groupconsisting of reverse osmosis, ultrafiltration, microfiltration,nanofiltration, electrodialysis, electrodeionization, pervaporation,membrane extraction, membrane distillation, membrane stripping andcombinations thereof.
 5. The method of claim 3 wherein the membraneseparation process is selected from the group consisting of reverseosmosis, ultrafiltration, microfiltration and nanofiltration.
 6. Themethod of claim 1 wherein the inert fluorescent tracer is selected fromthe group consisting of 3,6-acridinediamine,N,N,N′,N′-tetramethyl-,monohydrochloride; 2-anthracenesulfonic acidsodium salt; 1,5-anthracenedisulfonic acid; 2,6-anthracenedisulfonicacid; 1,8-anthracenedisulfonic acid;anthra[9,1,2-cde]benzo[rst]pentaphene-5,10-diol, 16,17-dimethoxy-,bis(hydrogen sulfate), disodium salt; bathophenanthrolinedisulfonic aciddisodium salt; amino 2,5-benzene disulfonic acid;2-(4-aminophenyl)-6-methylbenzothiazole;1H-benz[de]isoquinoline-5-sulfonic acid,6-amino-2,3-dihydro-2-(4-methylphenyl)-1,3-dioxo-, monosodium salt;phenoxazin-5-ium, 1-(aminocarbonyl)-7-(diethylamino)-3,4-dihydroxy-,chloride; benzo[a]phenoxazin-7-ium, 5,9-diamino-,acetate;4-dibenzofuransulfonic acid; 3-dibenzofuransulfonic acid;1-ethylquinaldinium iodide; fluorescein; fluorescein, sodium salt;Keyfluor White ST; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt; C.I. Florescent Brightener230; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetasodiumsalt; 9,9′-biacridinium, 10,10′-dimethyl-, dinitrate;1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-ribitol;mono-, di-, or tri-sulfonated napthalenes selected from the groupconsisting of 1,5-naphthalenedisulfonic acid, disodium salt (hydrate);2-amino-1-naphthalenesulfonic acid; 5-amino-2-naphthalenesulfonic acid;4-amino-3-hydroxy-1-naphthalenesulfonic acid;6-amino-4-hydroxy-2-naphthalenesulfonic acid;7-amino-1,3-naphthalenesulfonic acid, potassium salt;4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid;5-dimethylamino-1-naphthalenesulfonic acid; 1-amino-4-naphthalenesulfonic acid; 1-amino-7-naphthalene sulfonic acid; and2,6-naphthalenedicarboxylic acid, dipotassium salt;3,4,9,10-perylenetetracarboxylic acid; C.I. Fluorescent Brightener 191;C.I. Fluorescent Brightener 200; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-,dipotassium salt; benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2(2-phenylethenyl)-, sodium salt;1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt; pyranine; quinoline;3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide; xanthylium,9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt;phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride; C.I.Fluorescent Brightener 235; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt; xanthylium, 3,6-bis(diethylamino)-9-(2,4-disulfophenyl)-,inner salt, sodium salt; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodium salt; Tinopol DCS; benzenesulfonic acid,2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis, disodium salt;benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt;7-benzothiazolesulfonic acid,2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt;and all ammonium, potassium and sodium salts thereof; and all mixturesthereof.
 7. The method of claim 1 wherein the inert fluorescent traceris selected from the group consisting of1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)-Dribitol; fluorescein; fluorescein, sodium salt; 2-anthracenesulfonicacid sodium salt; 1,5-anthracenedisulfonic acid;2,6-anthracenedisulfonic acid; 1,8-anthracenedisulfonic acid; mono-,di-, or tri-sulfonated napthalenes selected from the group consisting of1,5-naphthalenedisulfonic acid, disodium salt (hydrate);2-amino-1-naphthalenesulfonic acid; 5-amino-2-naphthalenesulfonic acid;4-amino-3-hydroxy-1-naphthalenesulfonic acid;6-amino-4-hydroxy-2-naphthalenesulfonic acid;7-amino-1,3-naphthalenesulfonic acid, potassium salt;4-amino-5-hydroxy-2,7-naphthalenedisulfonic acid;5-dimethylamino-1-naphthalenesulfonic acid; 1-amino-4-naphthalenesulfonic acid; 1-amino-7-naphthalene sulfonic acid; and2,6-naphthalenedicarboxylic acid, dipotassium salt;3,4,9,10-perylenetetracarboxylic acid; C.I. Fluorescent Brightener 191;C.I. Fluorescent Brightener 200; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-(4-phenyl-2H-1,2,3-triazol-2-yl)-,dipotassium salt; benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt;1,3,6,8-pyrenetetrasulfonic acid, tetrasodium salt; pyranine; quinoline;3H-phenoxazin-3-one, 7-hydroxy-, 10-oxide; xanthylium,9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-, chloride, disodium salt;phenazinium, 3,7-diamino-2,8-dimethyl-5-phenyl-, chloride; C.I.Fluorescent Brightener 235; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[bis(2-hydroxyethyl)amino]-6-[(4-sulfophenyl)amino]-1,3,5-triazin-2-yl]amino]-,tetrasodium salt; benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[4-[2-hydroxypropyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-, disodium salt; xanthylium,3,6-bis(diethylamino)-9-(2-4-disulfophenyl)-, inner salt, sodium salt;benzenesulfonic acid,2,2′-(1,2-ethenediyl)bis[5-[[4-[(aminomethyl)(2-hydroxyethyl)amino]-6-(phenylamino)-1,3,5-triazin-2-yl]amino]-,disodiumsalt; Tinopol DCS; benzenesulfonic acid,2,2′-([1,1′-biphenyl]-4,4′-diyldi-2,1-ethenediyl)bis-,disodium salt;benzenesulfonic acid,5-(2H-naphtho[1,2-d]triazol-2-yl)-2-(2-phenylethenyl)-, sodium salt;7-benzothiazolesulfonic acid,2,2′-(1-triazene-1,3-diyldi-4,1-phenylene)bis[6-methyl-, disodium salt;and all ammonium, potassium and sodium salts thereof; and all mixturesthereof.
 8. The method of claim 1 wherein the inert fluorescent traceris selected from the group consisting of 1,3,6,8-pyrenetetrasulfonicacid tetrasodium salt; 1,5-naphthalenedisulfonic acid disodium salt(hydrate); xanthylium, 9-(2,4-dicarboxyphenyl)-3,6-bis(diethylamino)-,chloride, disodium salt;1-deoxy-1-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl) -D-ribitol; fluorescein; flurorescein, sodium salt; 2-anthracenesulfonicacid sodium salt; 1,5-anthracenedisulfonic acid;2,6-anthracenedisulfonic acid; 1,8-anthracenedisulfonic acid; andmixtures thereof.
 9. The method of claim 1 wherein the taggedfluorescent agent comprises a water-soluble polymer tagged with at leastone fluorescent group.
 10. The method of claim 9 wherein the fluorescentgroup is selected from the group consisting of hydroxy allyloxypropylnapthalimide quat, 4-methoxy-N-(3-N′N′-dimethylaminopropyl)napthalimide,2 hydroxy-3-allyloxypropyl quat, 8-(3-vinylbenzyloxy)-1,3,6-pyrenetrisulfonic acid; 8-(4-vinylbenzyloxy)-1,3,6-pyrene trisulfonic acid,8-(allyloxy)-1,3,6-pyrene trisulfonic acid, 1-(substituted) naphthalene,9-(substituted)anthracene, 2-(substituted) quinoline monohydrochloride,2-(substituted) benzimidazole, 5-(substituted) fluorescein,4-(substituted) coumarin, coumarin derivatives,3-(substituted)-6,7-dimethoxy-1-methyl-2(1H)-quinoxazolinone, mixturesthereof and derivatives thereof.
 11. The method of claim 9 wherein thewater-soluble polymer comprises a monomer selected from the groupconsisting of acrylamide, acrylic acid, methacrylamide, vinyl acetate,dimethylaminoethyl acrylate methyl chloride quaternary salt,dimethylaminoethyl acrylate benzyl chloride quaternary salt,diallyldimethyl ammonium chloride, N-vinyl formamide; dimethylaminoethylmethacrylate methyl chloride quaternary salt, dimethylaminoethylmethacrylate benzyl chloride quaternary salt, methacrylamino propyltrimethyl ammonium chloride, acrylamidopropyl trimethyl ammoniumchloride, and combinations thereof.
 12. The method of claim 1 whereinthe tagged fluorescent agent comprises a copolymer of acrylate andacrylamide tagged with a hydroxy allyloxypropyl napthalimide quat in anamount of about 2% or less by weight of the copolymer.
 13. The method ofclaim 1 wherein the inert fluorescent tracer and the tagged fluorescentagent are each introduced into the feed stream in an amount from about 5ppt to about 1000 ppm.
 14. The method of claim 1 wherein the inertfluorescent tracer and the tagged fluorescent agent are each introducedinto the feed stream in an amount from about 1 ppb to about 50 ppm. 15.The method of claim 1 wherein the inert fluorescent tracer and thetagged fluorescent agent are each introduced into the feed stream in anamount from about 5 ppb to about 50 ppb.
 16. The method of claim 1wherein the inert fluorescent tracer and tagged fluorescent agent areadded to a formulation capable of treating scaling and/or fouling priorto addition to the feed stream.
 17. The method of claim 1 furthercomprising the step of: (h) determining the ratio of the amount of inertfluorescent tracer to the tagged fluorescent agent based on theconcentration of the inert fluorescent tracer and the concentration ofthe tagged fluorescent agent in each of the streams where theconcentrations were measured.
 18. A method for detecting damage to amembrane used in a membrane separation process comprising the steps of:(a) providing an industrial process, wherein within said industrialprocess there are feed streams comprising one or more solutes in anaqueous liquid; (b) providing a membrane capable of removing solutesfrom a feed stream by separating said feed stream into a first streamand a second stream, wherein said first steam is the permeate stream andsaid second stream is the concentrate stream; (c) selecting an inertfluorescent tracer and a tagged fluorescent agent; wherein the selectionis made such that it is known in advance that one or both of said inertfluorescent tracer and said tagged fluorescent agent are not capable ofpassing through the membrane into the permeate stream; (d) introducingthe inert fluorescent tracer and tagged fluorescent agent into the feedstream; (e) providing one or more fluorometers, to enable the detectionof the fluorescent signal of the inert fluorescent tracer in the feedstream and in the permeate stream and the detection of the fluorescentsignal of the tagged fluorescent agent in the feed stream and in thepermeate stream; (f) using the one or more fluorometers to detect thefluorescent signal of the inert fluorescent tracer in the feed streamand in the permeate stream and to detect the fluorescent signal of thetagged fluorescent agent in the feed stream and in the permeate stream;wherein, if one or both of the fluorescent signals of the inertfluorescent tracer and the tagged fluorescent agent are found in thepermeate then this indicates the membrane is damaged in some way.